Recently, an electric vehicle has been drawing attention with rising interest in resource constraint or an environmental issue. The electric vehicle is a vehicle that uses electric energy as an energy source and uses an electric motor as a power source. In the electric vehicle, the motor is driven using power stored in an installed battery. In this way, the electric vehicle may travel several tens to several hundreds of kilometers by being charged once.
A plug-in scheme and a wireless power transfer scheme have been known as a power feeding scheme of feeding power for charging the installed battery to the electric vehicle. The plug-in scheme is a scheme of directly performing power feeding by inserting a power feeding plug at a distal end of a power source cord connected to a commercial power supply into a power feeding plug of the electric vehicle. The wireless power transfer scheme is a scheme of wirelessly performing power feeding using electromagnetic induction, a resonance phenomenon of an electromagnetic field, etc. from a power transmitter installed on a ground to a power receiver installed in the electric vehicle.
There is a known technology related to a wireless power transfer system that includes a power transmission unit having a power transmission coil and a power reception unit having a power reception coil which wirelessly receives power from the power transmission coil. As such a technology, for example, in a power transfer system described in Patent Literature 2, a relation between a misalignment and reflected power obtained when power output from the power transmission unit is reflected to return to the power transmission unit is prepared in advance. A misalignment between the power transmission coil and the power reception coil is examined based on the relation and detected actual reflected power. In a parking assistance device described in Patent Literature 3, a positional relation between a power reception unit of a vehicle and a power transmission unit of a power transmitter is detected based on an image captured by a camera. The vehicle is controlled such that the vehicle is guided to the power transmission unit based on a result of the detection. In a parking assistance device described in Patent Literature 4, a relation between a power reception condition and a distance between a power transmission unit and a power reception unit is determined in advance in response to an output of a height sensor that detects a change in a vehicle height. Positioning is performed based on the power reception condition and the output of the height sensor using this relation.